The present invention relates to vacuum degassing systems generally, and more particularly to systems for degassing mobile phase materials in chromatographic applications. This invention also relates to methods for degassing mobile phase materials.
Many chemical applications, particularly analytical applications, which involve the use of liquid solvents, reactants, or the like wherein the presence of dissolved gases, particularly air, is undesirable. An example of such an application relates to the mobile phase in high performance liquid chromatography where the presence of even small amounts of dissolved gases, and in particular oxygen, can interfere with the accuracy and sensitivity of the results obtained. For example, air dissolved in the mobile phase can manifest itself in the form of bubbles, with the bubbles causing measurement noise and drift as the mobile phase passes through a detector. If the dissolved species is chemically active, as in the case of oxygen in air, unwanted changes or deterioration in the mobile phase can occur. The detrimental effect of the dissolved species typically relates to the relative concentration of the species in the mobile phase. Such undesirable species are typically removed by a known degassing process. Correspondingly, it is desirable to utilize an efficient and effective degassing system to reduce dissolved gas concentration in respective mobile phases.
A number of techniques for degassing liquids have been developed, including heating or boiling the liquid to be degassed, exposing the material to a reduced pressure environment or vacuum, exposure to ultrasonic energy, or combinations thereof. As conventionally applied, however, these traditional techniques have generally fallen short of the desired degree of degassing efficiency.
Another technique that has been developed more recently is vacuum degassing through a membrane apparatus. A common such application utilizes a tubular length of relatively small diameter, thin-walled, semi-permeable synthetic polymer resin material contained within an enclosed chamber and held under a reduced pressure or vacuum. To perform the degassing, the liquid to be degassed is caused to flow through the chamber, thereby allowing gases to pass through the tube while preventing the liquid from doing so. In some applications, modules employing relatively flat gas-permeable membranes have been utilized for degassing various liquids.
Systems developed to date, however, have a number of problems and limitations associated therewith. For instance, such systems typically need to be relatively large to obtain a desired level of degassing due to the relatively low degassing efficiency of such systems. In flat membrane applications, systems proposed to date require support-type structures to assist in supporting the membrane both in fabrication and use. Such support structures add complexity and cost to the degassing components, as well as introducing additional parts which may be susceptible to breakage in use. Furthermore, materials commonly utilized for such membranes have limited gas permeability characteristics whereby the membranes are desirably less than about 10 micrometers in thickness to provide adequate degassing functionality.
It is therefore a principle object of the present invention to provide a degassing system for degassing liquids in a highly efficient manner by utilizing a compact flat membrane degasser.
A further object of the present invention is to provide a compact degassing system for use in a liquid chromatography environment.
A still further object of the present invention is to provide a compact degassing system utilizing a self-supported, relatively flat membrane.
A yet further object of the present invention is to provide a compact degassing system utilizing a degassing membrane material which enhances degassing efficiency.
Another object of the present invention is to provide a method for casting and attaching a membrane to a supporting porous structure in a compact degassing system. Such a membrane/film structure constitutes a self-supporting film structure.
By means of the present invention, an improved flow-through degassing system utilizing a relatively flat membrane in a compact degassing component is provided for increasing the efficiency of degassing various mobile phases in liquid chromatography applications. Such improved degassing means is achieved by forming a self-supporting thin membrane in a compact degassing component, which membrane is gas-permeable and liquid-impermeable. Such efficiency is further achieved through the use of an improved membrane material, which is preferably a perfluorinated copolymer such as TEFLON AF(trademark). Through the use of such copolymers, it has been determined that it is possible to increase the thickness of the membrane while retaining, or even improving upon, typical degassing performance. A particular advantage achieved through such an invention is the enhanced durability of such a self-supporting membrane, as well as elimination of the necessity to include distinct support structures for supporting the thin membrane in the degassing component. Such improvements are achieved without either reduction or compromise in degassing performance.
One embodiment of the degassing system of the present invention includes a degassing component having a degassing chamber therewithin, which chamber is divided into first and second portions by a self-supporting film, which is preferably gas-permeable and liquid-impermeable. The degassing component further includes fluid inlet and outlet channels which are in fluid communication with the first portion. The second portion of the degassing component is preferably accessible from a vacuum source. Preferably, the self-supporting film is between about 5 micrometers and about 500 micrometers in thickness, and more preferably between about 10 micrometers and about 125 micrometers in thickness. The film preferably comprises a perfluorinated copolymer, such as TEFLON AF(trademark). The degassing component preferably includes a permeable diffusion layer in the second portion disposed adjacent to the film, and between the film and the vacuum source. In preferred embodiments, the self-supporting film is at least partially adhered to the diffusion layer, which diffusion layer is preferably a composite polymeric material.
In another aspect of the invention, the self-supporting film is preferably formed through a thermal process whereby the perfluorinated copolymer is heated to a gel or molten phase and cast in the degassing chamber, and thereafter allowed to cool to form a self-supporting film. Most preferably, the heated perfluorinated copolymer is cast directly onto the diffusion layer, and thereafter allowed to cool to form the self-supporting film at least partially adhered to the diffusion layer.
An additional aspect of the present invention includes forming the self-supporting film through a solvent welding process whereby the perfluorinated copolymer is solvated in an appropriate solvent and subsequently cast in the degassing chamber, and thereafter dried to form the self-supporting film which is at least partially adhered to the diffusion layer.